Bacterial chemotaxis is a useful model system for investigating the molecular bssis of sensory transduction processes. The long-range goal of this project is to understand, through the use of genetic and biochemical technicques, the molecular events underlying chemotactic behavior in Escherichia coli. The primary objective of the present proposal is to undertake a systematic investigation of the role of protein methylation reactions in chemotaxis, which are believed to be important in enabling E. coli to undergo sensory adaptation. The genetic organization of loci that encode methyl-accpeting chemotaxis proteins (MCP's) will be studied by isolating new mutants defective in protein methylation. Mutants will be generated by localized mutagenesis with specialized lambda trqnducing phage to ensure tha a representative spectrum of mutant types is obtained. New mutations will be analyzed by deletion mapping and complementation tests to determine whether MCP loci are functionally complex. Mutant gene products will be examined by infecting ultraviolet-irradiated cells with lambdaMCP phages and analyzing labeled proteins by electrophoresis in sodium dodecyl sulfate-containing polyacrylamide gels (SDS-PAGE) to look for defects in methyl-accepting ability. These biochemical findings will be compared with the behavoiral defects of the mutants to investigate the relationship between MCP structure and function. The cheR, cheB, cheY, and cheZ gene products may be involved in modulating the steady-state level of MCP methylation in response to chemotactic stimuli. This oossibility will be tested by examining the MCP methylation state in a variety of che mutant strains. Attempts will be made to isolate new che mutants that are specifically defective in methylation control. These studies should provide valuable information about the way in which methylation-demethylation influences MCP signaling properties and the way this sytem is controlled by changes in the chemical environment of the cell.